1. Field of the Invention
The present invention relates to sodium N-acetylneuraminate.trihydrate. More specifically, the present invention pertains to sodium N-acetylneuraminate trihydrate which has low hygroscopicity and high storage stability as well as a method for preparing the same.
2. Description of the Prior Art
N-Acyl and O-acyl derivatives of polyhydroxy monoaminocarboxylic acid (neuraminic acid) are called sialic acids and are widely distributed throughout the living bodies of animals as constituents of mucopolysaccharides, glycoproteins and glycolipids.
The sialic acids are present at the ends of sugar chains of the glycoproteins and the glycolipids of animal cell membranes in large quantities, contribute to the occurrence of the negative charges on the cell surface, and play an important role in the specific recognizing-mechanism of the cell.
As already described above, the sialic acid acts as an acid because it has a carboxyl group. Thus, it can easily be converted into alkali metal salts or alkaline earth metal salts.
N-acetylneuraminic acid (hereafter referred to as "NANA" for simplicity) is a known compound and a typical example of a sialic acid. In addition, the present applicant already filed a patent application which claims an invention relating to an expectorant containing a compound represented by the following general formula as an effective component (Japanese Patent Publication for Opposition Purpose No. Sho 63-28411; now Japanese patent No. 1,478,542): ##STR2## (wherein, if n=1, Z represents hydrogen, lithium, potassium or sodium, or an ammonium or organic ammonium group or, if n=2, Z represents calcium, barium or magnesium.)
However, N-acetylneuraminates (salts) are in general hygroscopic and it is difficult to handle them in powder form. Therefore, their preservation and storage are correspondingly very difficult.